1. Field of the Invention
The present invention relates to a driving device in which a driven member is moved to a prescribed direction by using a reciprocating motion of a drive source.
2. Background Information
Japanese Laid-Open Patent Application Publication No. H11-41953 discloses a conventional driving device in which a rod (driving member) and a slider (driven member) are frictionally engaged with a prescribed pressing force via a spring. This conventional driving device disclosed in this reference is configured to control a speed of expansion and contraction of a piezoelectric element (drive source) coupled to the rod. The slider is moved without slipping when the rod is moved in a low speed in a driving direction. On the other hand, the rod is moved in a high speed in a direction opposite the driving direction so that the rod slips on the slider due to an inertia force in the slider. Therefore, the slider is driven in one direction (in the driving direction) by the reciprocating motion of the rod. In such conventional driving device, since the pressing force is fixed regardless of the direction of movement of the rod during the reciprocating motion of the rod, when the rod moves in the direction opposite the driving direction, a relatively large energy is lost by the friction. However, if the pressing force is reduced in order to prevent the energy loss caused by the friction, slippage may occur between the rod and the slider due to the pressing force being insufficient.
Therefore, Japanese Laid-Open Patent Application Publication No. 2005-57907 discloses another conventional driving device in which an additional piezoelectric element is used instead of a spring for applying a pressing force to a slider so that the pressing force can be controlled according to the driving direction of a rod. More specifically, the conventional driving device disclosed in this reference is configured to control the additional piezoelectric element such that the pressing force is applied when the rod moves in the driving direction and the pressing force is not applied when the rod moves in the direction opposite the driving direction. Therefore, the energy loss due to the friction can be prevented.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved driving device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.